An acidic, low molecular weight (M.W. 11500) clacium binding protein has been found in rat hepatomas and mouse sarcomas, which might be tumour-specific, because it has not been found in several normal adult or fast growing fetal tissues. It is proposed that by the use of selective immunosytochemistry and sensitive radioimmunoassay to examine both the incidence an quantity of this protein in a wide variety of tumour cells, and to make a determined effort to see whether it can be found in any normal embryonic or adult tissue. This will involve screening of normal and embryonic tissue, as well as solid tumours, and both cells of human and animal origin in vitro. The point during carcinogenesis in vitro when it first makes is appearance will be established, and its appearance will be correlated to neoplastic indices such as loss of proliferative calcium dependence, growth in agar, and ability to form tumours in athymic nude mice. It is also hoped to determine the intracellular localisation of this protein using immunocytological procedures.